package task;

import java.util.Scanner;

public class Task5_6 {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int n = input.nextInt();
        System.out.println(sumAdd(n));

    }
    public static  int sumAdd(int n){
        if(n == 0){
            return 0;
        }
        return n + sumAdd(n - 1);
    }
}
